It really depends on your project. Do you want to create a structure for a stage, a small installation.... Do you need solid bars or flexible strips.
For prototyping, a teensy 3.x in USB (15$) and APA102 strips would work: http://www.madmapper.com/2015/09/30/ard ... apper-2-1/
That's the minimal investment.
If you want to do a stage project with LEDs you'll have to use USB DMX or ethernet. Using ethernet has no cost and makes cabling easier. You can use an Advatek Pixelite (50-200$ depending on the number of outputs) to convert ethernet DMX (ArtNet) to LEDs protocol (WS2811-2812 / APA102, LPD...). That's cheap and reliable equipment. Then you can buy flexible DIGITAL
So there are plenty of solutions depending on your project. In any case, for big installations, the budget is not MadMapper or the LED controller/USB DMX stuffs, the cost is the LED hardware.